DS-8201a exhibited a potent antitumor activity in a broad selection of HER2-positive models and favorable pharmacokinetics and safety profiles. The results demonstrate that DS-8201a will be a valuable therapy with a great potential to respond to T-DM1-insensitive HER2-positive cancers and low HER2-expressing cancers. Clin Cancer Res; 22(20); 5097-108. ©2016 AACR.

A major limitation of traditional chemotherapy for cancer is dose-limiting toxicity, caused by the exposure of non-tumor cells to cytotoxic agents. Use of molecular targeted drugs, such as specific kinase inhibitors and monoclonal antibodies, is a possible solution to overcome this limitation and has achieved clinical success so far. Use of an antibody-drug conjugate (ADC) is a rational strategy for improving efficacy and reducing systemic adverse events. ADCs use antibodies selectively to deliver a potent cytotoxic agent to tumor cells, thus drastically improving the therapeutic index of chemotherapeutic agents. Lessons learned from clinical failure of early ADCs during the 1980s to 90s have recently led to improvements in ADC technology, and resulted in the approval of four novel ADCs. Nonetheless, further advances in ADC technology are still required to streamline their clinical efficacy and reduce toxicity. [fam-] Trastuzumab deruxtecan (DS-8201a) is a next-generation ADC that satisfies these requirements based on currently available evidence. DS-8201a has several innovative features; a highly potent novel payload with a high drug-to-antibody ratio, good homogeneity, a tumor-selective cleavable linker, stable linker-payload in circulation, and a short systemic half-life cytotoxic agent in vivo; the released cytotoxic payload could exert a bystander effect. With respect to its preclinical profiles, DS-8201a could provide a valuable therapy with a great potential against HER2expressing cancers in clinical settings. In a phase I trial, DS-8201a showed acceptable safety profiles with potential therapeutic efficacy, with the wide therapeutic index.

Trophoblast cell surface antigen 2 (TROP2) is highly expressed on various epithelial tumors and correlates with poor prognosis. We developed the novel TROP2-directed antibody-drug conjugate (ADC), datopotamab deruxtecan (Dato-DXd, DS-1062a), with a potent DNA topoisomerase I inhibitor (DXd), and evaluated its antitumor activity and safety profiles in preclinical models.The pharmacologic activity and mechanism of action of Dato-DXd were investigated in several human cancer cell lines and xenograft mouse models including patient-derived xenograft (PDX) models. Safety profiles were also assessed in rats and cynomolgus monkeys.Dato-DXd bound specifically to TROP2 and was internalized into tumor cells followed by intracellular trafficking to lysosome and DXd release, which induced DNA damage and apoptosis in TROP2expressing tumor cells in vitro. Dato-DXd exhibited in vivo antitumor activity with DNA damage induced by the accumulated DXd in TROP2-expressing xenograft tumors, but neither isotype control IgG-ADC nor anti-TROP2 antibody had this effect. Dato-DXd also showed potent antitumor activity with tumor regression in several TROP2-expressing xenograft tumors including NSCLC PDX models. Safety profiles of Dato-DXd in rats and cynomolgus monkeys were acceptable.Dato-DXd demonstrated potent antitumor activity against TROP2-expressing tumors by efficient payload delivery into tumors and acceptable safety profiles in preclinical models. These results suggest Dato-DXd could be a valuable treatment option for patients with TROP2-expressing tumors in the clinical setting. delivery into tumors Binding to TROP2, internalization into cancer cells and payload release Dato-DXd (Anti-TROP2 ADC) TROP2 Cancer cell Nucleus DNA topoisomerase I inhibition leading to DNA damage and apoptosis Tumor regression Cancer cell

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Purpose: HER3 is a compelling target for cancer treatment; however, no HER3-targeted therapy is currently clinically available. Here, we produced U3-1402, an anti-HER3 antibody-drug conjugate with a topoisomerase I inhibitor exatecan derivative (DXd), and systematically investigated its targeted drug delivery potential and antitumor activity in preclinical models.Experimental Design: In vitro pharmacologic activities and the mechanisms of action of U3-1402 were assessed in several human cancer cell lines. Antitumor activity of U3-1402 was evaluated in xenograft mouse models, including patientderived xenograft (PDX) models. Safety assessments were also conducted in rats and monkeys.Results: U3-1402 showed HER3-specific binding followed by highly efficient cancer cell internalization. Subsequently, U3-1402 was translocated to the lysosome and released its payload DXd. While U3-1402 was able to inhibit HER3activated signaling similar to its naked antibody patritumab, the cytotoxic activity of U3-1402 in HER3-expressing cells was predominantly mediated by released DXd through DNA damage and apoptosis induction. In xenograft mouse models, U3-1402 exhibited dose-dependent and HER3-dependent antitumor activity. Furthermore, U3-1402 exerted potent antitumor activity against PDX tumors with HER3 expression. Acceptable toxicity was noted in both rats and monkeys.Conclusions: U3-1402 demonstrated promising antitumor activity against HER3-expressing tumors with tolerable safety profiles. The activity of U3-1402 was driven by HER3mediated payload delivery via high internalization into tumor cells.